An optical disc, approximately 64 mm in diameter, having a recording capacity capable of recording music sound signals for 74 minutes or longer, is currently well known. This small-sized optical disc, termed a Mini-Disc (registered trademark), is classified into a replay-only disc, having data recorded as pits, and a recording and/or reproducing disc, having data recorded by a magneto-optical recording (MO) system and which may thus also be reproducible. The following description is directed to a small-sized recording and/or reproducing disc, referred to below as a magneto-optical disc. With this magneto-optical disc, the track pitch, the recording wavelength of the recording laser light or the NA of the objective lens have come to be ameliorated in order to increase disc's recording capacity.
A magneto-optical disc of an initial stage, in which groove recording is carried out with the track pitch of 1.6 μm, is termed the first generation MD. The physical format of this first generation MD is prescribed as follows: The track pitch is 1.6 μm and the bit length is 0.59 μm/bit. The laser wavelength λ is set to λ=780 nm and the numerical aperture of the optical head NA is set to NA=0.45. The recording system employed is the groove recording system in which a groove (i.e. a groove formed on the disc surface) is used as a track for recording and/or reproduction. The address system employed is a system employing the wobbled groove in which a single-spiral groove is formed on a disc surface and in which a wobble as the address information is formed on both sides of this groove. Meanwhile, in the present specification, the absolute address recorded by the wobbling is termed an ADIP (Address in Pre-Groove).
In the conventional first generation MD, an EFM (8 to 14 modulation) system is employed as the recording data modulating system. As the error correction system, ACIRC (Advanced Cross Interleave Reed-Solomon Code) is used. For data interleaving, a convolution type data interleaving is used. In this manner, data redundancy amounts to 46.3%.
In the first generation MD, the data detection system is a bit-by-bit system, while the disc driving system used is the CLV (Constant Linear Velocity) system. The linear velocity of the CLV system is 1.2 m/sec.
The standard data rate during recording and/or reproduction is 133 kB/sec, while the recording capacity is 164 MB (140 MB for MD-DATA). The minimum data re-write unit (cluster) is constructed by 36 sectors composed of 32 main sectors and four link sectors.
Moreover, in these days, the next-generation MD, having a recording capacity further improved over the first generation MD, is being developed. Such an MD in which the medium is unchanged from the conventional medium (disc orb cartridge), and in which the modulation system or the logical structure is changed to increase the data recording capacity to for example 300 MB is now contemplated. This MD is referred to below as the next-generation MDI. The physical parameters of the recording medium are the same, the track pitch is 1.6 μm, the laser light wavelength λ is such that λ=780 nm and the numerical aperture of the optical head NA is such that NA=0.45. The recording system used is the groove recording system. The address system used is the ADIP. Thus, the structure of the optical system, ADIP address readout system and the servo processing in the disc driving device are similar to those of the conventional mini-disc. In this manner, compatibility with the conventional disc (first generation MD) is maintained. That is, the mode of the next generation MD may co-exist with the conventional mode.
If a reproducing apparatus for coping only with the first generation MD is unable to co-exist with the new mode, that is, unable to reproduce the next generation MD1, an alerting area having recorded the information alerting that the UTOC or replay of the first generation MD is not possible may be recorded with the conventional recording format, in which case it may be seen that reproduction is not possible with the reproducing apparatus adapted for coping only with the first generation MD because the UTOC or the alerting area may be read even with such reproducing apparatus adapted for coping only with the first generation MD.
Meanwhile, it may be premeditated that an MD further increased in recording capacity as compared to the aforementioned next generation MD1, referred to below as a next generation MD2, may be offered to the market as a new recording medium in which the UTOC recording system is changed or the aforementioned alerting area is not provided and in which compatibility as to the outer shape or the optical system is maintained.
If, in such case, the next generation MD2 is loaded on a recording and/or reproducing apparatus capable of recording and/or reproducing the next generation MD1, the UTOC of the next generation MD2 cannot be accessed. Moreover, since there is provided no alerting area, it is impossible to alert to the user that the MD loaded is of such a sort that recording and/or reproduction is not possible with the recording and/or reproducing apparatus.